1. Field of the Invention
The present invention relates to an image forming apparatus using an electrophotographic method, and particularly relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine and the like.
2. Description of the Related Art
Conventionally, an electrophotographic process used in an electrophotographic image forming apparatus includes a charging step for uniformly charging a photosensitive member.
In a charging apparatus which performs the charging step, as a rotatable charging member, for example, a charging roller is in contact with the photosensitive member, and is rotatably driven by the photosensitive member. By applying a charging bias on the charging roller, a surface of the photosensitive member can be uniformly charged.
Since the charging roller is charged by contacting the photosensitive member on which a toner image is formed, a slight amount of a toner or an external additive adheres to the charging roller. If the toner and external additive accumulate on the surface of the charging roller by repetition of image formation, a situation may arise where the charging step cannot be suitably performed. More specifically, if such a situation is left as is, a life of the charging apparatus cannot be extended.
Japanese Patent Application Laid-Open No. 8-95350 discusses an apparatus which is directed to resolving this problem by cleaning the charging roller with a rotating brush which serves as a cleaning rotating member.
More specifically, by pressing the rotating brush toward the charging roller by a spring, the rotating brush obtains a driving force from traction with the charging roller surface and rotates. By employing such a configuration, the drive mechanism of the rotating brush can be simplified, and costs can be reduced.
The apparatus discussed in Japanese Patent Application Laid-Open No. 8-95350 employs a method in which the rotating brush obtains the driving force from the charging roller surface, such that the rotating brush is firmly pushed against the charging roller.
However, for the apparatus discussed in Japanese Patent Application Laid-Open No. 8-95350, deformation of a fiber portion of the rotating brush tends to increase during repeated image formation. Further, because the fiber portion deformation is not uniform in a longitudinal direction of the rotating brush, uneven contact occurs between the rotating brush and the charging roller in the longitudinal direction. This phenomenon is significant when a fiber length of the rotating brush is long, and cannot be ignored.
If peripheral speed of the rotating brush fluctuates due to such uneven contact, a “relationship between the peripheral speed of the rotating brush and the peripheral speed of the charging roller” which is predetermined so that cleaning performance by the rotating brush is suitable, breaks down.
As a result, the rotating brush can no longer suitably clean the charging roller and causes cleaning defects.
To prevent the peripheral speed fluctuation of the rotating brush, as one method, a driving force is externally input so that the rotating brush rotates at a certain peripheral speed. However, even if this method is employed, the above-described problem still cannot be resolved.
The reason for this is that since the charging roller is rotatably driven along with the rotation of the photosensitive member by obtaining the driving force from the surface of the photosensitive member, the charging roller may slip on the photosensitive member for some reason and the peripheral speed of the charging roller fluctuates.
Thus, the “relationship between the peripheral speed of the rotating brush and the peripheral speed of the charging roller” which is predetermined so that the cleaning performance by the rotating brush is suitable breaks down, and the cleaning defects may occur.